This invention relates to rapid cold-set binders. In a particular aspect, this invention relates to a foundry composition characterized by rapid setting at room temperature.
Cores useful in making metal castings are customarily made by placing a foundry aggregate, usually silica sand which has been admixed with a suitable binder, against a shape or pattern and then hardening the binder, as by polymerization. The resulting core is a self-supporting structure which forms a part of a mold assembly.
Various sands are used for making cores. The cores themselves are made by a variety of processes employing a wide variety of binders. Three of the many processes in commerical use today are the so-called cold box process, no-bake process and the rapid no-bake process.
The cold box process is one in which sand is admixed with a suitable resinous binder composition; the mixture is blown into a core box, and is then gassed with a suitable vapor phase catalyst to cure the binder. By such process, which is described, for example, in U.S. Pat. No. 3,409,579, a core of sufficient hardness to be stripped from the core box is produced in a matter of seconds.
The no-bake process is one in which a resinous core binder is admixed with a catalyst and sand and the mixture placed in a core box. The core cures at ambient temperatures but much more slowly than in the cold box process, over a period of hours or even days. After a suitable period of time, such as two hours, the core can generally be stripped from the core box, but requires further cure time.
The rapid no-bake process is similar to the no-bake process, but the character of the resin and the amount and type of catalyst employed are such that a core is formed and may be stripped from the core box in a matter of a few minutes. The bench life, or time period during which a sand-resin mixture may be kept before the reaction proceeds to a detrimental extent prior to placing the mixture into the core box, generally decreases rapidly when the catalyst and resin are adjusted to provide very rapid set times.
These processes have been very successful. However, those wherein isocyanates are used are unsatisfactory in that they become air pollutants in the work area and can cause severe problems in industrial hygiene. Accordingly, a need exists for a non-polluting foundry aggregate composition.